Cellular responses to a wide variety of physiological stresses (e.g. hyperthermia, viral infection, surgical trauma) include specifically enhanced expression of several protein families, the stress or heat shock proteins (HSPs). Stress responses function to protect cells from injurious accumulation of abnormal or denatured proteins. Constitutively expressed stress proteins also function in many ongoing processes (e.g as molecular chaperons). The proposed research will examine stress protein expression in the rat olfactory epithelium (OE). The OE is unique among vertebrate neuronal tissue in its continual turnover of sensory neurons (ORNs) and in the direct contact of these neurons with the external environment and stressing agents within it. OE stress responses appear to reflect these unique properties: following olfactory bulbectomy and exposure to several drugs, ORNs do not show stress protein responses; but OE nonneuronal populations, which show no ongoing turnover, do. In addition, under normal, nonstressing conditions an ORN subpopulation (less than or equal to 0.2% of the total) is uniquely labeled by a monoclonal antibody (Mab2A4) which reacts with constitutive (HSC70) and stress-induced (HSP70) members of the 70kDa HSP family. This labeling allows the axonal projection pathways of the 2A4(+)ORNs to be traced to their targets: 2-3 glomeruli, consistently located, in each olfactory bulb. The proposal has 7 Specific Aims grouped into 3 categories: 1) To use the 2A4(+)axonal immunoreactivity (IR) to examine the plasticity and specificity of the 2A4(+) bulbar innervation patterns. 2) To examine inducible OE stress responses and correlate these with survival of the various OE component cell types. 3) To undertake initial studies to characterize 2A4 + ORNs and their olfactory function. These Specific Aims are directed toward the long-range goals of understanding cell interactions involved in OE turnover processes under normal and experimental conditions, understanding the OE-bulbar interactions occurring during these processes, and determining what distinguishes the 2A4(+) ORNs from the remaining, 2A4(-), ORNs and how this is related to olfaction. The proposed research will examine the IRs of Mab 2A4 and other stress protein antibodies in normal OE and in OE subjected to hyperthermia, reduced 02, and nonlethal levels of methyl bromide. It will examine olfactory bulb innervation by 2A4(+)axons during development and following surgical manipulation. Autoradiographic birthdating will determine ORN age at the time of initial 2A4 labeling and at long post- bulbectomy survival periods. In situ hybridization studies will examine HSC70 and HSP7O messenger RNA and protein expression in the OE and in the 2A4(+)ORNs in particular.